Understanding your home’s plumbing rough-in makes renovation planning dramatically easier. Before opening walls for a kitchen or bathroom renovation, knowing what’s there — and what code requires — saves expensive surprises.
Ontario Plumbing Code Basics
Plumbing in Ontario is governed by the Ontario Building Code (Part 7) and must be performed by or under the supervision of a licensed plumber. Rough-in work must pass inspection before walls are closed.
Drain, Waste, and Vent (DWV) System
Drainage pipes carry waste water from fixtures to the municipal sewer or septic system. In Ontario homes:
- 4" ABS (black plastic) or cast iron: main drain/stack
- 3" ABS: toilet drain (minimum)
- 2" ABS: lavatory, tub/shower drain, kitchen sink with dishwasher
- 1.5" ABS: lavatory only (minimum)
Venting is critical and often misunderstood. Every fixture trap must be vented to prevent siphoning (which lets sewer gas enter the home). In Toronto’s tight Victorian housing stock, wet venting and air admittance valves (where code-permitted) are common solutions when conventional venting to roof is impractical.
Critical spec: Drain slope must be 1/4" per foot (2%) minimum and 1/2" per foot (4%) maximum for 4" and smaller pipes. Too little = blockage. Too much = solids left behind.
Supply Lines
Modern Ontario homes use PEX (cross-linked polyethylene) for supply lines — flexible, freeze-resistant, and easy to work with in renovations. Older homes have copper, which can be retained or replaced.
Cold water pressure: 40–80 PSI normal range. A pressure reducing valve (PRV) is required when municipal pressure exceeds 550 kPa (80 PSI).
Hot water temperatures: Ontario code requires thermostatic mixing valve at bathtubs to prevent scalding — maximum 49°C at tub/shower in new construction and renovations.
When Relocating Fixtures
Moving a toilet requires a new 3" drain stub-up at the new location — typically $800–$2,500 in labour depending on access. Moving a kitchen sink across the room means extending drain lines under the floor — $1,000–$3,000+ depending on basement accessibility.
These costs explain why plumbing layout changes significantly affect renovation budgets.
Ontario plumbing questions, contractor recommendations, and project experiences at home.renovation.reviews.
LF Builders — GTA renovation specialists, 50+ years.